A new director, Alfonso Cuarón, makes all the difference in Harry Potter and the Prisoner of Azkabanthis series' The Empire Strikes Back, so to speak. About halfway through the new film, Malfoy the school bully (Tom Felton) murmurs, "God, this place has gone downhill." He's a swine, yet there's something to what he says.

Cuarón, who previously made A Little Princess and Y tu mamá también, is less dazzled by the upper-crust swank of Hogwarts than was the previous helmsman, Chris Columbus. For much of the movie, the three heroes dress in Levis or sweatshirts instead of school robes.

Harry (Daniel Radcliffe), Hermione (Emma Watson) and the woeful comic Ron Weasley (Rupert Grint) spend a lot of time hanging out on the fringes of the school; they're taking time away from the professors, who are rarely what they seem. The train that leads to the magical academy for wizards is less like a Victorian toy train and more like British Rail.

All this smudging and fading doesn't make the school less magic. Cuarón observes neolithic stonesStonehenge stonesscattered about a ruined abbey with cloisters, outside Hogwarts. He suggests that the land around Hogwarts has been sacred for eons.

Still, the third Harry Potter movie has an undertone about the hypocrisies of the adult world and the dire penalties they inflict on innocent victimshow elastic their justice can be, depending on circumstances. Harry and his friends encounter werewolves and animaguses, wizards who can turn into animals. The plotting is a subtle reflection of the characters' own changing bodies as they grow into adolescence. Harry Potter and the Prisoner of Azkaban is Harry Potter's bar mitzvah movie; he's not a kid anymore.

The storytelling is sharper right from the beginning: a sequence inside the house of the Dursleys, Potter's hateful foster parents. Two televisions racket away in the kitchen, and the hand-held camera is jostled by those elephantine Dursley bodies. The cramped space grates on Harry; his household is not a joke to be borne patiently anymore.

He starts to shout at the loathsome Uncle Vernon (the marvelous pop-eyed Richard Griffiths) and Aunt Petunia (Fiona Shaw) and the even-more-revolting visiting Aunt Marge (Pam Ferris). We hear an adolescent rasp in Harry's voice, the exasperation familiar from those London-bred singers on British-invasion or punk-rock records. Radcliffe's Harry is still kind of a blank, but now he sounds alive.

On his way back to Hogwarts, Potter learns of more serious trouble. A maniac wizard named Sirius Black (Gary Oldman) has escaped from the maximum-security prison of Azkaban. Hogwarts is on yellow alert. Azkaban's jailers, floating specters that look like bundles of midnight-colored ragsdementorsfly over the school, on the lookout for Black. They keep attacking Harry by accident. The young wizard goes through his round of classes, frightened by both these patrolling ghouls and the madman wizard Black, an associate of the dread Voldemort.

Cuarón uses frosty, northern light for the exteriors. Under such clear cold illumination, the characters look more frail and bruised. Hogwarts, with its rocks and rooks and lonely vistas, is like the dry-stick and hedgerow country on the cover of Led Zeppelin IV.

Screenwriter Steve Kloves has cleaned up the book's tangled thickets, speeding over J.K. Rowling's lamentable tendency to have her characters stand stock-still and explain the plot. And Cuarón uses overlapping and overheard dialogue to accelerate the film. He even gives the movie a Mexican touch: in the basement of the mystical sweets shop Honeydukes at Hogmead village, one glimpses a tray of Day of the Dead sugar skulls. Older viewers can get great pleasure of a clutch of celebrity teachers. Oldman, Alan Rickman, David Thewlis and Timothy Spall share the same stage at one point, but it'll be the dazzle of the effects that children talk about, not Cuarón's taste and personality.

Despite the kind of soundtrack John Williams must compose during his lunch break, this new Harry Potter is completely engrossing in a way the first two movies weren't. Going a little darker, but not too much, the talented Cuarón has made a movie for the children who grew up reading the Potter saga, children who are little children no more.

Harry Potter and the Prisoner of Azkaban (PG; 136 min.), directed by Alfonso Cuarón, written by Steven Kloves, based on the novel by J.K. Rowlings, photographed by Michael Seresin and starring Daniel Radcliffe, Richard Griffiths and Emma Watson, opens Friday countywide.